Donepezil HCI (Aricept®) is an FDA-approved drug now used to enhance memory in patients with Alzheimer's disease. The aim of this project is to examine the effects of Donepezil HCI (Aricept®) on memory induced brain activation patterns in the context of a double-blind, crossover trial of patients with multiple sclerosis (MS). We will perform task activation experiments involving two cognitive domains. The proposed work on MS patients should yield new information regarding functional anatomic relationships during cognitive activity, and how these relationships change as a function of drug treatment.